Endocrine Abstracts

Introduction: Diabetes Insipidus (DI) is the inability of the kidneys to concentrate urine. This is due to decreased production of Anti-diuretic Hormone (ADH) from the posterior pituitary gland (cranial DI) or decreased tubular sensitivity to ADH (nephrogenic DI) or a mixed picture.

Case: A 53-year-old male presented with several-months history of polyuria and polydipsia. He had constant thirst and had to void urine four times at night. He did not have diabetes mellitus or previous urological ailments. He is a smoker but not on any regular medication. He had no significant findings on physical examination.

Investigation and management: He had kept a 24-hour fluid input-output diary which revealed an input of 6000 ml and output 7900 ml. His serum osmolality was normal at 287 mOsm/kg with low urine osmolality of 105 mOsm/kg. A repeat test revealed a raised serum osmolality of 297 mOsm/kg with an inappropriately low urine osmolality of 143 mOsm/kg. Further test demonstrated a low serum testosterone level (5.9 nmol/L) in the presence of inappropriately normal Luteinising Hormone and Follicle Stimulating Hormone levels, suggesting hypogonadotrophic hypogonadism. His prolactin, thyroid and adrenal function tests were normal. He had a water deprivation test during which time his serum osmolality climbed to 299 mOsm/kg while his urine osmolality climbed to a maximum of 304 mOsm/kg at first then rose to 559 mOsm/kg only after a 2 mcg injection of Desmopressin. A diagnosis of diabetes insipidus was made. An ultrasound scan revealed normal kidneys. An MRI scan revealed a complex cyst arising from his hypothalamus. This awaits aspiration biopsy. He was started on Desmopressin with appreciable symptomatic improvement.

Conclusion: We present a rare combination of cranial DI and hypogonadotrophic hypogonadism secondary to a hypothalamic lesion. Other rare causes such as craniopharyngioma, lymphocytic hypophysitis and Erdheim-Chester disease make interesting differential diagnoses.